In on-orbit services, the relative position and attitude estimation of non-cooperative spacecraft has become the key issues to be solved in many space missions. Because of the lack of prior knowledge about manual marks and the inability to communicate between non-cooperative space targets, the relative position and attitude estimation system poses great challenges in terms of accuracy, intelligence, and power consumptions. To address these issues, this study uses a stereo camera to extract the feature points of a non-cooperative spacecraft. Then, the 3D position of the feature points is calculated according to the camera model to estimate the relationship. The optical flow method is also used to obtain the geometric constraint information between frames. In addition, an extended Kalman filter is used to update the measurement results and obtain more accurate pose optimization results. Moreover, we present a closed-loop simulation system, in which the Unity simulation engine is employed to simulate the relative motion of the spacecraft and binocular vision images, and a JetsonTX2 supercomputer is involved to conduct the proposed autonomous relative navigation algorithm. The simulation results show that our approach can estimate the non-cooperative target’s relative pose accurately.

In this article, we present a free-vertex tetrahedral finite-element representation of irregularly shaped small bodies, which provides an alternative solution for estimating asteroid density distribution. We derived the transformations between gravitational potentials expressed by the free-vertex tetrahedral finite elements and the spherical harmonic functions. Inversely, the density of each free-vertex tetrahedral finite element can be estimated via the least-squares method, assuming a spherical harmonic gravitational function is present. The proposed solution is illustrated by modeling gravitational potential and estimating the density distribution of the simulated asteroid 216 Kleopatra.

In the past decades, space missions to small bodies (Galileo, OSIRIS-REx, Hayabusa, Hayabusa2, Chang’ e 2, Rosetta, etc.) have enriched us greatly with a lot of new knowledge on our solar system. In situ observations of these missions have revealed the extreme complexity and remarkable diversity of the spatial environment around their target asteroids. A study on the motion of objects in such complex environments is of great importance for understanding the evolution history of surface/sub-surface materials on the asteroids. Establishing a reasonable dynamic model is obviously the most important step. This paper proposes a method for tracking the motion of an object near the surface of an arbitrary asteroid. This method combines the irregular shape, an unlimited rotational state and asymmetric gravitational field, which are three key factors that dominate the complex movement of an object on and off the asteroid’s surface. The gravitational attraction and potential are computed using the polyhedral method with corrections for the possible singularities. The asteroid’s surface is then approximated using a continuous and smooth surface, and the parametric representation forms of the body are derived based on polynomial series. An event-driven scheme is designed, so that the orbital motion and surface motion are processed separately by checking the triggering events. The algorithm was implemented using C++. Benchmarking tests are organized on a local cluster, showing a satisfying performance in both accuracy and efficiency. And this method was also applied to motion control of surface detectors.